Since 1950's the electrical industry has been using Audio Frequency Load Control (AFLC) system for load balancing control in electrical power distribution networks. In general, a AFLC system works to inject electrical signals of fixed audio frequencies, e.g. 1,042 Hz or 1,050 Hz typically, at the high voltage distribution network equipment, which are then distributed to the low voltage networks and then further to the points of load where AFLC frequency sensitive relays (AFLC relays) responsive to the AFLC signals are installed. An AFLC relay is tuned to respond to a specific AFLC carrier or “ripple” frequency that is modulated with a digital data signal. The digital data signal carries instructions for the AFLC relay to turn a power sub-circuit on and off, as such load shedding heavy loads such as hot water heaters, ovens, air-conditioners, etc. This enables network operators to have point of use control of heavier electrical loads to balance the power generation and usage.
In more recent times, to optimize the operating conditions for maximum energy efficiency in the usage, transmission, and delivery of alternating current (AC) electrical power, network operators have been installing switched capacitor power factor correction (PFC) equipment in electrical power distribution networks. The PFC equipment basically comprises capacitors that are in shunt with the mains network and operate at the mains frequencies, e.g. 50 Hz and 60 Hz. The presence of the PFC capacitors, however, presents a very low impedance to the higher AFLC frequencies, e.g. a factor of over twenty impedance reduction in the cases of 1,042 Hz and 1,050 Hz. This in turn bypasses the high frequency AFLC signals to neutral and/or short-circuiting the AFLC signals, reducing the amplitude of the AFLC signals enough to cause unreliable operation of the AFLC relays and malfunction to the AFLC network load balancing scheme. To mitigate this problem, one well-established legacy solution is to install large and heavy passive bypass or blocking filters at the PFC installations. This solution, however, adds size, weight, and cost to the PFC installation.